<!DOCTYPE html>
<html>
<head>
    <meta charset="utf-8"/>
    <meta name="viewport" content="width=device-width, initial-scale=1">
    <title>JavaScript变量</title>
</head>
<body>
<script type="text/javascript">
    {
        var a = 12;
        var a = "zhangsan";
        alert(a);

        let b = 12;
        alert(b)

        const c = 21;
        alert(c);
    }
    alert(a + "|" + b + "|" + c);
</script>
</body>
</html>